1. Field of Invention
The invention relates generally to the field of data and content delivery. In one exemplary aspect, the invention relates to the delivery of optical and non-optical content via a delivery network which is dynamically adjustable to accommodate varying proportions of each.
2. Description of Related Technology
Content distribution networks (such as e.g., Cable Television (CATV) systems) provide content from various content sources at a network headend to a plurality of subscriber devices. In the exemplary context of CATV, delivery to the subscriber devices was accomplished by transmitting radio frequency (RF) signals over coaxial cables.
Such prior art RF networks require the use of separate frequency bands for delivery of content, and for various types of communications between network entities. In practice, this distinct frequency band architecture is implemented largely through the use of frequency separating filter apparatus (e.g., so-called “diplexers”, which in effect multiplex two or more signals into disjoint frequency bands through use of, inter alia, low- and high-pass filters). However, such diplexer apparatus are generally (i) fixed in terms of frequency characteristics; (ii) consume a significant amount of otherwise available bandwidth (due to e.g., the required precision associated with the filter so as to avoid the undesirable phenomenon of “group delay”, the rolloff characteristics of the filters, etc.).
As an extension of the foregoing, many modern systems now utilize digital light pulses transmitted over optical fibers to more efficiently provide content in a first portion of the network towards the core (e.g., a DWDM or other optical “ring”), and then utilize existing coaxial cabling for providing content to the subscriber's individual homes (due to the large amount of extant coaxial cable in the premises). This is referred to as a “hybrid fiber/coaxial cable network” or HFC network.
Specifically, a hybrid fiber/coax network typically includes a head end that broadcasts programming over the network to subscribers in a downstream direction. A first portion of the network utilizes optical links to connect the headend with a number of geographically dispersed distribution nodes (referred to as “optical distribution nodes”, “ODNs”, or simply “nodes”). At the ODNs, signals from the headend that carry the programming are converted from optical signals to electrical signals. A second portion of the network utilizes coaxial links to connect the nodes with subscriber equipment, as well as to other nodes.
Optical fiber permits transmission over longer distances and at higher bandwidths (data rates) than other forms of carriage (such as coaxial cable). However, the incremental installation costs of new optical fiber versus use of existing fiber and coaxial cabling have thus far inhibited utilization of optical fibers any deeper into the network than from network hubs to the nodes which service multiple hundreds of homes in a neighborhood or service area. Installation of fiber to each existing premises is largely cost prohibitive.
As noted above and illustrated in FIG. 1, existing networks provide content signals to a plurality of subscribers via fiber to a first node. The first node converts optical signals to and from RF electrical signals, and amplifies these signals in order to distribute-content to and collect data from a plurality of homes serviced by the node. A plurality of amplifier devices are provided to amplify RF signals so that it may be pushed further out into the network edge (i.e., on to additional homes serviced by the node). This cascading approach has the cost benefit of requiring optical fiber only to the node. However, this system suffers many of the same problems of the traditional all-coaxial cable network, in that the delivery of the content as RF signals between repeater amplifiers is limiting.
Under another prior art scheme (commonly referred to as “node plus zero”), optical fiber is run out to each node of the network, and then is delivered passively to each downstream customer. The term “passive” in this context refers to the situation where no power consuming devices are present in a link other that those at the endpoints. Node plus zero in this context refers to architecture between an optical-to-electrical or electrical-to-optical conversion device (node) and a coaxially-fed endpoint. See for example the Aurora Networks' “Fiber Deep™” architecture, which uses a traditional HFC node but does not use repeater amplifiers. This “node plus zero” approach ostensibly provides the benefits of shortened runs of optical fiber, and the simplicity of passive delivery. However, in practice, this approach has a number of salient drawbacks, including: (i) the requirement for a separate laser and receiver for each node (and in the network head end), which can be quite costly, and (ii) the need to adjust, inspect, and possibly align the laser frequently, thereby incurring a high degree of technician labor and maintenance resources, and reducing the robustness of the system.
Other prior art approaches seek to add additional bands of service (e.g., above existing or legacy service bands) through use of filtration. Specifically, in such prior art approaches, a series of diplex filters are used at various locations throughout the network so as selectively create new bands in tandem with extant or legacy bands. In this case, the newly added signals (bands) are introduced at one of the termination points, and effectively sent through the network distribution cascade to the opposite termination point. This necessitates (aside from points where the signal power is split are passive and bidirectional in nature and as full-band connections, do not employ or require filters) use of filtration and/or other design considerations at effectively every repeater amplifier within the network cascade, which is highly cost intensive. Moreover, in order to ensure adequate performance (including the undesirable phenomenon of group delay), very precise and high performance diplex filters are required, thereby increasing cost.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an improved cascading network architecture. Ideally the improved network would build on top of and utilize existing infrastructure to the maximum extent practical to support a slow and manageable migration to optical technologies (i.e., providing optical fiber to all amplifiers within the network) over time, not require large capital investments in restructuring the existing network, while also maintaining RF connectivity to the homes uninterrupted. Additionally, the improved network would utilize more recent advances in signal conditioning and processing to provide more efficient and flexible connectivity, and the incrementally added infrastructure would further be comparatively maintenance free (so as to avoid, e.g., the aforementioned frequent alignment or other maintenance dictated by prior art multi-band systems).